A study on transmission of noise in railway tunnel

Pao Yue-kong Library Electronic Theses Database

A study on transmission of noise in railway tunnel


Author: Fung, Wai-sun William
Title: A study on transmission of noise in railway tunnel
Degree: Eng.D.
Year: 2009
Subject: Hong Kong Polytechnic University -- Dissertations.
Railroad tunnels -- Noise.
Railroads -- Noise.
Sound -- Transmission -- Measurement.
Department: Dept. of Mechanical Engineering
Pages: xii, 234 leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2276597
URI: http://theses.lib.polyu.edu.hk/handle/200/3888
Abstract: With the demand for rapid transportation by people and goods within cities and among countries, the number of railway lines has been increased tremendously during the last fifty years. More and more overhead and underground railway stations are being built everyday. In Hong Kong, citizens travelling between towns and districts, or even across the boundary to China, are now relying heavily on the mass transit railway system. Passengers are now aware on the requirement for a better trains comfort as compared with vehicles on road or on board of planes than that of forty or fifty years ago. More recently, railway operators focus on developing and providing multimedia broadcasting, wireless networks and passenger information in train compartments and stations. However, less research work has been carried out to study the noise level or speech intelligibility in train compartments in order to ascertain the suitability in installing such address systems. A high quality of speech intelligibility is definitely required to facilitate an effective communication in train compartments. Noise inside a train mainly comes from the rolling noise. With train travels in tunnels, the reverberant sound fields that excited between the tunnel walls and train bodies will enhance this noise levels that penetrated through the train body into the train car. A high noise level within the train will then occur as a result of high rolling noise when train is travelling at a high speed. As litter literature and limited research work have been carried out and explored in this area, it is the intention in the thesis to investigate such phenomenon with those related studies and established models. Though, most of the train tunnel is of circular shape in nature, experimental and analytical study carried out in the thesis shows that the circular shape tunnel can be modelled by a rectangular duct using the well known and established image source method with a tolerable accuracy. In addition, in comparing the numerical results due to the proposed approximate method with the proprietary software, a reasonably good agreement is obtained. The initial work in the thesis is to investigate the noise level of a moving train and to establish an empirical relationship between the train speed and its reverberant sound field for an existing rolling stock. Secondly, the use of a rectangular model to approximate a real circular tunnel is conducted experimentally. Finally, the results obtained from the analytical study of a rectangular model show that not only it can provide valuable information in studying the reverberation sound field, but also it can also offer useful information in studying the sound propagation in an L-shaped space. The findings in the thesis can become a study guide for acoustic engineers in planning the construction of a new railway line. The result can provide useful information in carrying out further study on the speech intelligibility of a train compartment. It can be used as a guideline in attenuating any high noise level in a railway tunnel. It can also provide a good insight for designers and architects in predicting and analysis the behaviour of sound propagation in long enclosures for entertainment, and for announcement and emergency excavation purposes. The exploration on the study of the L-shaped enclosure is set as a preliminary study for an insert section in a rectangular enclosure that can be further approximated as a train situated in a circular tunnel. The experimental and laboratory work of the thesis was carried out in the Mass Transit Railway Corporation's premises and inside the anechoic chamber of the Hong Kong Polytechnic University respectively.

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